Pay once for an app that is in Windows Phone + Windows + Xbox stores
We should be able to allow people to pay once for our apps and then they can get both version of our apps for Windows Phone or Windows 8 without having to make them pay twice.
The Store now supports the concept of universal Windows apps to allow you to share consumer purchases across apps that use the same PFN (Product Family Number). You can currently use this app linking to link purchases/IAPs across Windows Phone Store apps (starting with Windows Phone 8.0 apps and games) and Windows Store apps (starting with Windows 8.0).
For more information, please see the following blog post: http://blogs.windows.com/windows/b/buildingapps/archive/2014/04/14/dev-center-now-open-for-windows-phone-8-1-and-universal-windows-app-submissions.aspx
Hefin Dsouza commented
Although sometimes we might price our apps at different values what Microsoft could do is allow some mechanisms to offer a discount if the user has purchased one version of the app and he wants to purchase another one.
FYI - Moved this to the Store forum and tweaked the title based on comments.
Should be done for XBLIG, Windows Phone, Windows Store devcenter registration!
This has already been done with Galactic Reign and others. However, actual support for this would set the platform apart. Additional support for buy once, play anywhere on Windows Phone, Xbox, and Windows 8 would be absolutely amazing.